1. Field of Invention
The present invention relates generally to the field of nanolithography. More specifically, the present invention is related to self-assembled nanolithography using a polystyrene-polydimethylsiloxane or other Si-containing block copolymer, in which the orientation of the block copolymer domains can be controlled.
2. Discussion of Prior Art
The growing demand for nanoscale fabrication methods, combined with the inherent feature-size limitations of optical lithography and the low throughput of electron-beam lithography, have motivated a search for cost-effective nanoscale fabrication technologies, including nanoimprint lithography, dip-pen nanolithography, and block copolymer lithography. In the case of block copolymer lithography, the use of a chemical or topographical template enables control over the long range order of the self-assembled patterns, providing a simple and scalable nanopatterning method in which the feature sizes and geometries are controlled via the chain length and volume fractions of the block copolymer.
In block copolymer lithography, arrays of holes or dots may be defined using a spherical-morphology block copolymer or a cylindrical-morphology block copolymer with the cylinders oriented perpendicular to the substrate. In contrast, patterns consisting of parallel lines may be defined using a cylindrical-morphology block copolymer with the cylinders parallel to the surface or a lamellar block copolymer with a perpendicular orientation. Such patterns have been templated using both chemical and topographical substrate features. For example, lamellar poly (styrene-b-polymethyl methacrylate) (PS-PMMA) patterns have been templated using a chemical pattern formed using extreme ultraviolet interference lithography (EUV-IL) or electron-beam (e-beam) lithography, and have attracted much attention due to their high aspect ratio and absence of defects. However, this process requires template generation on the same lengthscale as the period of the block copolymer. On the other hand, well-ordered arrays of in-plane cylinders templated by larger scale topographical patterns have been demonstrated by several groups. Horizontal cylinders from diblock copolymers such as poly (styrene-b-ethylene propylene) (PS-PEP) and PS-PMMA have been successfully aligned in topographical templates. The templates have critical dimensions an order of magnitude or more than the block copolymer period, and can be made by optical lithography.
In all these examples the removal of one block leaves a structure made from the other block, typically PS, that could be used as a mask for pattern transfer into a functional material. PS is, however, a rather poor mask, having a glass transition temperature of 100° C. and relatively low etch resistance. It is therefore desirable to instead use a block copolymer containing one etch-resistant block in order to facilitate pattern transfer. In addition, in these block copolymers a small but significant number of defects (dislocations or disinclinations) remain, which is undesirable for nanolithographic applications. The defect population is related to the Flory-Huggins interaction parameter, χ, which describes the driving force for microphase separation in the block copolymer. Block copolymers with higher χ have a higher driving force for reducing the defect population, and are therefore more desirable for achieving long range ordering.
The following references provide a general background teaching in the area of block copolymer lithography:
The paper of Sundrani et al. titled “Guiding polymers to perfection: macroscopic alignment of nanoscale domains” teaches a method wherein nanoscale diblock copolymer domains are aligned within topographical trenches via top-down/bottom-up hierarchical assembly. Sundrani et al. teach that depending on trench depth and amount of deposited polymer, aligned domains are (1) confined to the trenches or (2) expanded across the trenches frequently with (3) a complete absence of defects.
The paper of Black titled “Self-aligned self assembly of multi-nanowire silicon field effect transistors” discusses the efficacy of diblock copolymer self assembly for solving key fabrication challenges of aggressively scaled silicon field effect transistors.
The paper of Cheng et al. titled “Nanostructure engineering by templated self-assembly of block copolymers” discusses the formation of defects in a self-assembled array of spherical block-copolymer microdomains using topographical templates to control the local self-assembly.
The paper of Sundrani et al. titled “Spontaneous spatial alignment of polymer cylindrical nanodomains on silicon nitride gratings” teaches a simple method to align lying-down cylindrical domains of PS-b-PMMA in the trench regions of 555 nm deep silicon nitride gratings without the aid of an external orientation field.
The paper of Angelescu et al. titled “Macroscopic Orientation of Block Copolymer Cylinders in Single-Layer Films by Shearing” teaches shear-induced ordering of cylindrical block copolymers.
Whatever the precise merits, features, and advantages of the above cited references, none of them achieves or fulfills the purposes of the present invention.